After James Watson and Francis Crick saw the DNA pictures taken by Rosalind Franklin, they tried several different models until they finally realized that DNA is in the form of a double helix with two strands of nucleotides.

14th Dec, 1955

46 Chromosomes in Humans is Discovered

Joe Hin Tjio, a NIH (National Institution of Health) researcher, discovered the actual number of chromosomes in humans was 46. He published his findings sometime in April 1956.

31st Dec, 1955

DNA Polymerase

Arthur Kornberg isolates DNA polymerase, an enzyme that will be used for many kinds of recombinant DNA techniques and sequencing. (year 1955, actual month and day not known)

2nd Apr, 1956

Joe Hin Tjio Publishes findings on 46 Chromosomes

7th Mar, 1958

Semiconservative Replication of DNA

Matthew Meselson and Franklin Stahl discover that DNA replicates semiconservatively, each strand of DNA molecule from the parent generation pairing with a strand from the daughter generation. (actual date not known)

8th Mar, 1961

mRNA Function is Discovered

Sydney Brenner, Francois Jacob, and Matthew Meselson discover that mRNA is the molecule that delivers information from DNA to the ribosomes in the cytoplasm. (actual date not known)

9th Mar, 1966

Interpretation of Genetic Code

After several years, Marshall Nirenberg, Har Khorana and Severo Ochoa had finally cracked the genetic code. Showing how nucleic acids (and their four-letter alphabet) determine the order of the twenty kinds of amino acids in proteins.

10th Mar, 1968

First Restriction Enzymes Described

Several groups of researchers discovered that restriction enzymes recognize and cut specific short sequences of DNA. They’re found in bacteria, which use the enzymes to digest invading DNA. The enzymes became an important, early tool for mapping genomes. (actual date not known)

11th Mar, 1972

The First Recombinant DNA

The first production of recombinant DNA molecules, using restriction enzymes. Recombinant DNA technology involves the joining of DNA from different species and subsequently inserting the hybrid DNA into a host cell, often a bacterium. (actual date not known)

12th Mar, 1973

First Animal Gene Cloned

Stanford and UCSF researchers fused a segment of DNA containing a gene from the African clawed frog (Xenopus) with DNA from the bacterium E. coli and placed the resulting DNA back into an E. coli cell. The frog DNA was copied and the gene it contained directed the production of a specific frog protein. It was the first animal gene to be cloned. (actual date not known)

13th Mar, 1975

DNA Sequencing

Sanger developed a slightly different protocol for sequencing DNA. Sanger's method, where a marker attaches to the growing ends of DNA chains, is used most commonly in labs now. (Sanger is his name) (actual date not known) (actual years were from 1975 -77)

14th Mar, 1976

First Genetic Engineering Company

Herbert Boyer, one of the creators of recombinant DNA technology in the early 70s, founded Genentech with venture capitalist Robert Swanson. (actual date not known)

15th Mar, 1977

Discovery of Introns

Richard Roberts' and Phil Sharp's labs showed that eukaryotic genes contain many interruptions, called introns. Human genes are on average interrupted about 10 times, and the introns typically contain about 90 percent of the DNA sequence in the whole gene. (actual date not known)

15th Mar, 1981

First Transgenic Animals

Scientists had been able to add new genes to bacterial cells for several years. In the early 80s, they figured out how to add stably-inherited new genes to animals. The first such "transgenic animals" were mice and fruit flies. (actual date not known)

16th Mar, 1983

First Genetic Disease Mapped

A genetic marker linked to Huntingtons disease was found on chromosome 4 in 1983, making Huntingtons disease the first genetic disease mapped. (actual date not known)

17th Mar, 1983

Invention of PCR

PCR, the polymerase chain reaction, is a technique for amplifying DNA that greatly increased the pace of genetic research. In a few hours, PCR can make billions of copies of a specific segment of DNA. (actual date not known)

18th Mar, 1987

First Human Genetic Map

The first comprehensive genetic map of human chromosomes was based on 400 restriction fragment length polymorphisms (RFLP). A genetic map contains landmarks, like RFLPs, that occur in various forms. Tracking which variants are inherited in different people can be used to locate genes responsible for diseases. (actual date not known)

1st Oct, 1990

The Human Genome Project Begins

The Human Genome Project begins in 1990, the objective was to find and map every gene in the human genome. (the day is not known)

18th Mar, 1991

ESTs

An expressed-sequence tag (EST) is a stretch of DNA sequence made by copying a portion of an mRNA molecule. They were first proposed as a useful way to find genes in the genome in 1991. (actual date not known)

19th Mar, 1994

The Microbial Genome Program Begins

The DOE began a Microbial Genome Program in late 1994 to sequence the genomes of some bacteria.

20th Mar, 1995

Physical Map of Human Genome Is Completed

A physical map uses sequence-tagged sites (STSs) as markers to order large segments of DNA. One of the goals of the HGP was to complete a physical map with a marker every 100,000 base pairs by 1998. The map built by 1995 was a significant milestone toward that goal; it contained 15,086 STSs, spaced an average of 199,000 base pairs apart. (actual date not known)

21st Mar, 1996

Human Gene Map Created

Scientists created a map showing the locations of ESTs representing fragments of more than 16,000 genes from throughout the genome. (actual date not known)

22nd Mar, 1999

First Finished Sequence of a Human Chromosome

In 1999, the HGP completed the first finished, full-length sequence of a human chromosome, chromosome 22. This accomplishment demonstrated the power of the HGP method of clone-by-clone sequencing to obtain large amounts of highly accurate sequence. (actual date not known)

23rd Mar, 2001

First Draft of the Human Genome Sequence

The Human Genome Project international consortium published a first draft of the human genome sequence. The draft sequence covered more than 90 percent of the human genome. (actual date not known)

24th Mar, 2003

The Completion of the Human Genome Project

The International Human Genome Sequencing Consortium announced the successful completion of the Human Genome Project more than two years ahead of schedule and under budget. (actual date not known)